Digitizer with long contacts

ABSTRACT

1,157,641. Selective signalling. MOORE REED (INDUSTRIAL) Ltd. 15 July, 1966 [28 July, 1965], No. 32250/65. Heading G4H. A shaft 64, Fig. 6, position digitizer includes a 10&lt;SP&gt;-3&lt;/SP&gt; stage 61 in which brushes 0/9, 1/8, 2/7, 3/6, 4/5 and A, B, C, C o , C e  and COM, Fig. 5, are moved over stationary conductive segments 53, 54, 55, and 10&lt;SP&gt;-2&lt;/SP&gt; and 10-1 stages 62, 63 in which coded scales (e.g. as in Fig. 7, not shown, or as in Specification 1,135,204, which is referred to) are moved past stationary brushes, the arrangement being such that each stage produces a &#34; choosing signal &#34; which selects which brushes in the next higher stage are to be operative. The lowest denominational stage 61, Fig. 6, includes two brushes A, B, Fig. 5, whose outputs when suitably combined (Fig. 2, not shown) produce inverse signals a, b, Fig. 3a, which are used to energize the C e  and C 0  brushes respectively, Fig. 5, so that each numbered brush (e.g. 0/9) produces a signal when in a position corresponding to either of its numbers, the ambiguity being resolved by reference to brush C.

Dec. 30, 1969 s. EVANS 3,487,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 2 All IA y f (/m/n 5= 40) Dec. 30, 1969 D. s. EVANS 3,487,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 4 Dec.30, 1969 D. s. EVANS 3,437,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 5 m(an/ads afar/77rd [mg/b United States Patent US. Cl. 340-347 ClaimsABSTRACT OF THE DISCLOSURE A digitizer for converting an analogueposition into numerals with a plurality of contacts disposed on asupport so as to form at least a single contact track and a plurality ofparallel contact paths in that track with each contact trackrepresenting a numeral scale, a given division of length beingassociated with each numeral of that scale and each contact extendingalong its path for a distance equivalent to at least two of the givendivisions of length of the scale. Brushes fixed with respect to eachother are mounted for movement along the paths to produce signals whichare then transmitted to an external device for determining the numeralsinto which the position is converted.

This invention relates to contact type digitizers having contacts longerthan a scale division and to means for deriving therefrom signalscorresponding to each division.

In this specification the terms contact and brush will be used, theoperative association of a contact and a brush being referred to asconnection. The meaning I of such terms, with reference to electriccircuits, is wellknown but these terms will be used herein to refer alsoto other equivalent arrangements; such as, for example, optical,pneumatic, hydraulic and, particularly, to magnetic arrangements such asthose wherein a discrete area of a material in a certain magnetic statecorresponds to a contact and a sensor, corresponding to a brush, isprovided to obtain one or other of two signals (one of which maycorrespond to a state of no signal), according as the sensor is or isnot operatively coupled (connected) to such a discrete area of thematerial.

The base of a scale of nototion is the number of distinct digits whichare required to express all the readings of the scale; for example, abinary scale requires two digits (0 and 1), and a decimal scale requiresten digits (0, 1 9). In explaining this invention, reference will bemade to a decimal scale but it is to be understood that the principlescan be applied to scales having other bases.

The term reflected half-base will be used to describe apparatus in whichsignals related to the digits of the lower half of the base of a scaleare the same as those related to the corresponding complementary digitsin the upper half of the base.

In our co-pending patent application No. 26346/ 65 there is described areflected half-base digitizer wherein the lengths of the contacts do notexceed the track length corresponding to a single digit. The scaletracks are preferably arranged in closed circles. Since practicalconsiderations set a lower limit to the length of a convenientlyconstructed contact, there is a corresponding upper limit to theresolution of a practical scale, for any particular scale diameter.

One object of the invention is therefore to provide means wherebycontacts of a digitizer may be longer than the track lengthcorresponding to a single digit of the scale.

3,487,401 Patented Dec. 30, 1969 According to this invention, adigitizer comprises a track having a plurality of contact paths, thetrack corresponding to a scale of notation; contacts, corresponding tothe digits of the scale, distributed over the paths, each contactextending along its path by a distance substantially equivalent to atleast the distance corresponding to two adjacent digits of the scale;and a plurality of brushes mounted in fixed relationship with oneanother and in movable relationship with the paths, each path havingassociated therewith a brush capable of sequentially connecting with anddisconnecting from the contacts of the paths, both leading and trailingedges of the contacts having significance in reading; the contacts andbrushes being so relatively disposed that, in use, each brush carriesone of two signals, according as the brush is or is not connected to acontact, combined brush signals being logically related to the scalereading, as defined by the position of brushes along the track.

According to a first aspect of this invention, a digitizer may compriseas brush choosing drive means an arrangement as just described whereinthe said track has two parallel contact paths, respectivelycorresponding to two groups of digits into which the scale is separated;and wherein there is provided means whereby, in use, the brush signalsmay be connected to logic devices for combining the brush signals andproviding one of two choosing signals, according to the group of digitsin which the scale reading lies.

When the said drive means is to be connected to choosing means for areflected half-base digitizer, and/or a multiscale digitizer, thecontacts may be so arranged that the resulting choosing signals areinverted at the centre of the scale and/ or at the junction of twoscales.

When the contacts and brushes are conventional electric contacts andbrushes, the means for connecting each brush signal to the logic devicesmay comprise a return brush, so associated with the signal brush thatboth the signal and return brushes connect with one contactsimultaneously; the return brushes all being connected to a common line.A preferred alternative arrangement is, however, a continuous commoncontact, arranged along a path parallel to the said contact paths andhaving associated therewith a return brush connected to the common line,all the contacts being electrically connected together; such anarrangement makes it possible to avoid using a plurality of returnbrushes.

When equivalent optical, pneumatic or hydraulic devices are used ascontacts and brushes, the contacts will usually be apertures; thepassage of a beam of light, gas, or liquid through an aperture to areceiver providing one signal, while no beam reaching the receiver willcorrespond to the other signal.

Magnetic equivalents of contacts and brushes include arrangementsanalogous to a light-beam arrangement, the contact comprising a magneticcoupling between a transmitting device, disposed close to one side ofthe contact, and a receiving device similarly disposed on the other sideof the contact; and an arrangement wherein both transmitter and receiverare disposed on one side of the contact, the coupling between thetransmitter and the receiver being increased by the presence of thecontact. A single device may then, in effect, comprise both transmitterand receiver, the presence or absence of a contact affecting the signaltransfer properties of the device sufiiciently to provide twodistinguishable signals.

In the equivalent optical, pneumatic, hydraulic and magneticarrangements just described, the outputs of the receivers are connectedto the common line.

In certain cases, for example when a brush choosing driving means is tobe used in a reflected half-base digitizer, a yet further contact pathmay be arranged,

parallel to the driving contact paths and carrying complementingcontacts for distinguishing between the upper and lower groups of thescale base. This complementing path will have associated with it acomplementing brush, and the complementing contacts may be connected tothe common contact of the choosing drive track. Such an arrangement willhereinafter be referred to as a complementing signal means.

The nature of this invention will be made clear in the followingdescription, in which:

FIGURE 1 illustrates a brush choosing driving means, according to thisinvention;

FIGURE 2 shows logic devices connected to a brush choosing means, forselecting one of two brushes in response to drive signals from drivingmeans such as is shown in FIGURE 1;

FIGURES 3A and 3B show modifications of the arrangement of FIGURE 1;

FIGURE 4 shows an exemplary single decade refiected half-base digitizeraccording to this invention;

FIGURE 5 illustrates one decade of a multidecade decimal digitizer andchoosing drive track, according to this invention; and,

FIGURE 6 illustrates, in block form, a 1000 division digitizer accordingto this invention; and to the accompanying drawings in which:

FIGURE 7 illustrates another exemplary single decade reflected half-basedigitizer, particularly suitable for use in a thousand-divisiondigitizer;

FIGURE 8 shows, in block form, a logic circuit device for use with thedigitizer of FIGURE 7; and

FIGURE 9 shows a logic circuit of FIGURE 8 in greater detail.

One embodiment of the first aspect of this invention is illustrated inFIGURE 1, which shows a movable set of three contact paths 10, 11 and12, corresponding to the digits 0, 1 9, 1' of a decimal scale shown at13. The path 10 carries a continuous contact 110, forming a commonreturn connection. The path 11 carries three contacts 111, 112 and 113,positioned along the path so as to correspond with digits 1 and 2, and6, and 9 and 0 respectively; and the path 12 similarly carries contacts121, 122 and 123, corresponding to digits 2 and 3, 6 and 7, and 0 and 1.The length of each of the contacts on the paths 11 and 12 corresponds totwo digits. Three brushes A, B and COM, shown as solid dots in aposition corresponding to digit 0, are fixed relative to one another andare in movable relation to the contacts, along the paths. It will beseen that, as the brushes and contacts are moved relative to one anotherin the first decade 09, brush A is connected to the brush COM only whenits position corresponds to digits 2, 3, 6 and 7; similarly brush B isconnected to brush COM only when its position corresponds to digits 1,2, 5, 6 and 9, as shown for example by the open dots at digit 1. Signallines connected to brushes A and B will thus be correspondinglyconnected, or not connected, to a common signal line connected to brushCOM, and will carry one of two corresponding brush signals. These brushsignals can be combined, by means of known logic devices, to provide oneof two signals, a and b as shown at 14, according as the reading of thescale, as defined by the position of the brushes, is even or odd; thatis, the logic devices are arranged to perform the logical operations,

where A and B are the negation of A and B, and signifies disjunction(or).

FIGURE 2 shows a suitable logic device for performing the required logicoperations, together with brush choosing means to be driven by the logicdevice.

In FIGURE 2, signal lines designated A and B respectively, are forconnection to brushes A and B of FIGURE 1. Line A is connected directlyto AND gates 20 and 21 and through an inverter 22, to AND gates 23 and24; line B is connected directly to AND gates 20 and 24, and through aninverter 25 to AND gates 21 and 23. The inverters provide negationsignals A and E as shown and the AND gates 20, 21, 23 and 24 passsignals according to the respective logic relations AB, A E, AIS and AB,as shown. The signals from the AND gates are passed to switches 26 and27 of a bistable trigger circuit 28, capable of connecting one or theother of two signal lines 29 and 30 to a common line (not shown).

When the contacts and brushes comprise devices other than conventionalelectrical contacts and brushes, the common contact and the brush COMmay not be necessary, the common connection being otherwise provided;the operating principle will, however, be the same. Even withconventional contacts and brushes, the common contact 110 and brush COMmay be dispensed with, if a return brush is associated with each ofbrushes A and B, as hereinbefore described.

FIGURE 3A shows an alternative arrangement which is particularlysuitable for driving choosing means for a reflected half-base digitizer.

In FIGURE 3A, contact paths 10, 11' and 12' correspond to paths 10, 11and 12 of FIGURE 1, but contact pairs 130, 131 and 132 (corresponding tothe contact pairs of FIGURE 1) are spaced apart by path lengthsequivalent to three digits, instead of two digits, as in FIG- URE 1.Relative movement of the brushes and contact paths then result in brushsignals which, when combined by suitable logic devices, provide twosignals, a and b, as shown at 14'. It will be seen that the signals areinverted, when the brushes pass from digit 4 to digit 5 (that is, at thecenter of the base); and again, when the brushes pass from digit 9 todigit 0 (that is, from one decade to the next). The application of thisfeature will be made clear, hereinafter.

Instead of displacing the contacts on the path 12 or 12', relative tothose on path 11 or 11, as shown in FIGURES 1 and 3A, one of the brushesmay be displaced correspondingly. Such a modification, applied to thearrangement of FIGURE 3A, is shown in FIGURE 313, where the contacts onboth path 11 and path 12 each correspond to digits 2 and 3, 7 and 8 and2 and 3', respectively. The brushes A, B and COM are shown, as soilddots, in a position corresponding to digit 0 of the scale; since thecontacts on path 11 have been advanced by one digit, relative to FIGURE3A, brush B has also been advanced by one digit, relative to brush A.Since the common contact on path 10' is continuous, the position ofbrush COM is immaterial. Contacts and brushes so arranged will providebrush signals which can be combined, as described with reference toFIGURE 3A, to provide even and odd signals a and b as shown at 14 inFIGURE 3A.

If, for any purpose, more than two signals are required from a contacttrack and brush assembly such as has just been described, acorresponding number of parallel contact paths, with associated brushes,may be used. In such a case, the contacts on the individual paths may bealigned, after the manner described in connection with FIGURE 3B, andthe brushes staggered; such an arrangement of the contacts simplifiesthe manufacture of the contact assembly.

The principle of distributing contacts, corresponding to the digits of ascale of notation, over a plurality of parallel paths, and making thepath length of at least most of the contacts greater than the pathlength corresponding to a single digit, may be applied to digitizerscales; particularly to high resolution digitizers having a large number(for example 1000) divisions.

According to a second aspect of this invention a reflected half-basedigitizer comprises a plurality of contact tracks, the tracks incombination corresponding to a scale of notation whose digits areseparated into two complementary groups, each of which is related to acorresponding contact track; wherein each track comprises at least twoparallel paths, there being disposed on each path contacts separatedfrom one another along the path, and each path has movably associatedtherewith a brush capable of sequentially connecting with the contactson the path, each complementary pair of digits if the base of the scaleis even, or each complementary pair of digits and the center digit, ifthe base is odd, being associated with one brush; means being providedfor connecting brush choosing means to the digitizer whereby, when thetrue reading of the scale is represented by a particular digit, theoutput of the digitizer carries signals related only to the group ofdigits including said particular digit.

Choosing drive means and complementing signal means, as hereinbeforedescribed, may also be included. These means are respectively capable ofproviding drive signals, for driving choosing means for selecting adesired brush, and logic means control signals, for selecting one of thecomplementary pair of digits associated with the selected brush; bothactions being performed according to the reading of the brushes. Thevarious tracks of the digitizer, choosing drive means and complementiingsignal means will, in use, have fixed relationship one with another; thebrushes will have similar fixed relationship.

The second aspect of the invention will now be made clear by describingan exemplary embodiment of a single decade reflected half-basedigitizer, having conventional electric contacts and brushes. A secondrelated embodiment, wherein the digit contacts are distributed over asingle track will also be described.

The first embodiment is shown in FIGURE 4, wherein there are two contacttracks 40 and 41; track 40 comprises four paths 42, 44, 46 and 48, andtrack 41 comprises three paths 43, 45 and 47. Each of paths 42 to 46 hastwo digit contacts, shown in full lines and respectively identified bythe digits and 9, the contacts being disposed along the paths inpositions corresponding to the positions of the respective digits on thescale, shown at 49. Paths 47 and 48 have continuous contacts C and Cforming common contacts for the tracks 41 and 40, respectively. Contacts0 and 9 are connected to contact C and contacts 1 and 8 to C althoughnot so shown, contacts 2, 4, and 7 are also connected to C and 3 and 6to C It will be seen that track 40 carries contacts positionallycorresponding to a first group of digits comprising the even digits 0, 2and 4, in the lower half of the scale, and complementary digits 5, 7 and9 on the upper half of the scale. Track 41 similarly carries a secondgroup comprising the odd digits 1 and 3 and the complementary digits 6and 8. Track 40 will hereinafter be referred to as the evens tracks, andthe common contact C as the evens common contact; track 41 will bereferred to as the odds track, and contact C as the odds common contact.

With each of the paths 42 to 46 there is associated a brush, the brushesbeing respectively designated 0/9, 1/8, 2/7, 3/6 and 4/5, referring tothe digits corresponding to the contacts with which a designated brushcan connect. With the paths C and C there are similarly associatedcorresponding brushes C and C All the brushes are mounted in fixedrelationship one with another, the brushes being movable with respect tothe contact tracks, to establish a scale reading according to therelative position of the brushes and the contacts.

It will be seen that, when the brushes are in the positions shown inFIGURE 4 by solid dots, brush 0/ 9 is connected to brus'h if the brushesare moved to the positions shown by the open dots, brush 1/ 8 isconnected to brush C in either case, all other brushes are disconnectedfrom C and C Thus, the brushes 0/ 9 to 4/5 are capable of providing asignal indicating to which complementary pair of digts the scale is set,at any reading,

but there is a first ambiguity as to which of the two digits of the pairis the true reading. This first ambiguity can be resolved in a manner tobe explained hereinafter.

Each of the digit contacts shown in FIGURE 4 may be extended, in bothdirections, along the relevant paths, as indicated by the dotted lines;it may be possible to manufacture such extended contacts even if, in aparticular design, the path length corresponding to a single digit istoo small for a practicable contact of single digit size. With suchextended contacts, a second ambiguity will be introduced; when, forexample, the brushes are in the position shown in FIGURE 4 by the opendots, odds brush 1/8 is connected to odds common brush C as before, butevens brushes 0/9 and 2/7 are also connected to evens common brush C Itwill be seen that the second ambiguity always arises in the track whichis not related to the digit representing the true scale reading; theambiguity can therefore be resolved by isolating the common brush of thetrack in which the ambiguity arises. Such a choice of one of the commonbrushes C and C can be made by suitable brush choosing means, driven bymeans according to the first aspect of this invention, describedhereinbefore.

The second embodiment is illustrated in FIGURE 7 and comprises a singlecontact track having five code paths identified as V, W, X, Y and Z, anda common path COM; each path has an associated brush, the brushes beingidentified generally by 101. Portions of the paths correspond to thedigits 0 to 9 as indicated in FIGURE 7. The five code paths carrydiscrete contacts as shown, while the common path carries a continuouscontact.

Of the five code paths only three, namely W, X. and Z, have the edges oftheir contacts accurately positioned relative the scale (and thecorresponding brushes accurately aligned); the contacts and brushes ofthese three paths therefore determine changes from one digit to thenext. The function of the contacts on the two paths V and Y is todistinguish 0 and 9 from 4 and 5 and the positions of the edges of thesecontacts, and the alignment of the corresponding brushes, are thereforeless critical than in the cases of the paths W, X and Z. The theoreticalmaximum tolerance permissible in the brush positions on the paths V andY is il /2 divisions of the scale. The paths V and Y are complementaryand the signals of one could be derived electrically from those of theother; both are, however, preferably included so that there is never ano-signal condition, even for the digit 0.

All the contacts of the digitizer shown in FIGURE 7 are connectedtogether; the whole contact assembly may, in fact, be formed integrally,by printed circuit techniques or other known methods.

In use, the brushes corresponding to the paths V and Y may be connectedto a logic circuit} arranged to provide outputs corresponding to thedigits 0 to 4. A suitable logic circuit is shown at 102 in FIGURE 8 andincludes AND gates, an OR gate and inverters, respectively designated &,OR and Inv. The path Z provides complementing signals C and C, by meansof a logic circuit such as 103 in FIGURE 8.

In FIGURE 8 the signals from the digitizer paths are identified by thecorresponding letters; the inverses of signals W, X and Z are designatedW, X and Y.

When the digitizer of FIGURE 7 forms the low decade part of amultidecade digitizer, the cmplementing signals C and 6 may be used todrive choosing means for the next higher decade.

In FIGURE 4, the digit contacts of each track are arranged in staggeredformation, the corresponding brushes all being in line with the commonbrush. A reverse arrangement is, however, preferable, one at least ofthe brushes being displaced so that some, at least, of the contacts canbe arranged in line. One such arrangement is shown in FIGURE 5, wherethe contacts of an evens track, 50 and an odds track 51, are, in eachcase,

combined into single conducting bodies or layers, 53 and 54respectively, whereby all the digit contacts of a track are connected tothe corresponding common contact, in manufacture.

FIGURE 5 illustrates one decade (digits to 9, shown at 56) of amultidecade decimal digitizer, having an evens track, 50, an odds track51, and a choosing drive track, 52, all according to the principlesdescribed hereinbefore. Although the paths of the tracks are shown asstraight lines, it is to be understood that the paths are, in fact,closed circles, the tracks being continuous. The paths of the evens andodds track, and paths 10", 11 and 12' of the choosing drive track,correspond respectively with the paths designated by the same numbers inFIGURE 3A, 3B and 4; brushes associated with these paths also have thesame references as in FIGURES 3A, 3B and 4. Path 57 of the choosingdrive track 52 carries complementing contacts, a brush C beingassociated therewith.

It will be seen that, with the relative positions of the brushes andcontacts shown, neither brush A nor brush B is connected to brush COM;thus, logic devices such as are shown in FIGURE 2 will give a signalProviding brush choosing means, such as is shown in FIGURE 2, arearranged to select the evens common brush C and disconnect the oddscommon brush C brush 0/9 will be connected to brush C and the scalereading is either 0 or its complement 9. The ambiguity is resolved bythe complementing path 57, the complementing brush C being connected tothe brush COM, indicating that the true reading lies in the upper halfof the decade; the true reading is therefore 9.

If all the brushes are moved one digit to the right, in FIGURE 5, thechoosing drive signal will become and the odds common brush will beselected; the complementing contact C, however, now indicates that thetrue reading is in the lower half of the next higher decade and the truereading is digit 0 of that decade.

Digitizers such as that illustrated in FIGURE may have any number ofdivisions, so long as the total number is an integral multiple of thebase of the scale. Since the path length of the shortest contact istwice that corresponding to a single digit, a decimal digitizer having,for example 1000 divisions can. be manufactured sub stantially smallerthan a prior art digitizer of the same resolution. Such a 1000 divisiondigitizer is illustrated, in block form, in FIGURE 6.

In FIGURE 6, 61, 62 and 63 represent contact track assemblies andassociated brush assemblies, for scales having respectively onethousand, one hundred and ten divisions. Each track assembly comprises adisc of insulating material on which electrical contacts are laid out onclosed concentric paths. The contact disc of assembly 61 is rigidlymounted on a shaft 64, 64', for rotation therewith, the associatedbrushes being mounted in fixed po ition within the housing containingthe assembly so that, when the contact disc is rotated through aparticular angle relative to a datum position by means of the end 64 ofthe shaft, the contacts and brushes define a corresponding scalereading, one unit of the scale corresponding to of a revolution of theshaft 64. Assembly 61 thus gives signals corresponding to units of thescale.

Assembly '61 comprises three contact tracks, 65, 66 and 67; these trackscorrespond respectively to the tracks '52, 50 and 51 of FIGURE 5,repetitively extended to include one thousand digits. The common brushof track 65 (corresponding to brush COM of FIGURE 5) is connected to aterminal COM for connection to one side of a voltage source; the brushesA and B are connected, through corresponding terminals A and B, to achoosing logic and choosing device 68, such as is shown in FIGURE 2. The

choosing means chooses one or other of two lines, which are respectivelyconnected, through terminals C and C to corresponding common brushes (Cand C in FIGURE 5) of the evens contact track 66 and the odds contacttrack 67. The evens digit bushes (0/9, 2/7 and 4/5 in FIGURE 5) areconnected, through sets of terminals 69, to an amplifier 70, to whichthe odds digit brushes 1/8 and 3/6 in FIGURE 5) are also connected,through sets of terminals 71. The amplifier 70 is also connected toreceive complementing signals from the brush C, via terminal C, of thetrack 65. The amplifier 70 is similar to that described in ouraforementioned copending application and similarly comprises logicdevices, for directing a digit signal to the appropriate one of a set 72of t n unit digit output terminals according to the complementingsignal.

The contact discs of assemblies 62 and 63 are mounted in fixed positionswithin their housings, the associated brushes being rigidly mounted onthe shaft 64, 64', for rotation therewith. These assemblies are arrangedto act as reflected half-base digitizers, in the manner described in ourco-pending application No. 2.6346/65.

The assembly 62 has a digit track 73 having one hundred contacts,arranged in ten sequential decade sets, each contact corresponding toten units of the scale of assembly 61. The contacts of each set areconnected together in complementary pairs, symmetrically disposed aboutthe centre of the decade, and to corresponding pairs of contacts of theother sets. A pair of bushes is connected, through terminals 93, toterminals C and O, of the amplifier 70, which provide complementingchoosing signals, each of which corresponds to five units of the scaleof assembly 61 that is to one half of a division of the track 73; one orother of the pair of brushes is thereby chosen, according to the truescale reading, to provide a tens digit signal representing a decade ofthe scale of assembly 61.

A complementing track 74 has ten sequential complementing sets ofcontacts arranged to provide, in co-operation with a pair or brushesmovable by the shaft 64, one of two further complementing signals,according as the reading of the scale of track 73 is in a lower or upperhalf of a decade.

Signal lines connected respectively to the five complementary pairs ofcontacts of the track 73 are connected, through five sets of terminals76, to an amplifier 78; which amplifier also receives appropriatecomplementing signals from the complementing track 75, through. sets ofterminals 79. The amplifier operates in a manner similar to amplifier70, directing each tens digit signal to the appropriate one of a set 80of ten tens digit output terminals, according to the complementingsignal received through the terminals 79.

The assembly 63 has a digit track 81, having ten contacts, eachcorresponding to one hundred units of the scale of assembly 61, forminga single decade set; the contacts are connected together incomplementary pairs, symmetrically disposed about the centre of thedecade. A brush pair is driven by the complementing signals from thecomplementing track 75, each signal corresponding to one half divisionof the track 81, and thereby provides a hundreds digit signalrepresenting ten decades of the scale of assembly 61. A complementingtrack 83 has one complementing set of contacts arranged to provide, inco-operation with a pair of brushes movable by the shaft 64, one of twocomplementing signals, according as the reading of the scale of track 81is in the lower or upper half of the decade.

Five sets of terminals 84 convey signals from the five complementarypairs of contacts of track 81 to an amplifier 86; which amplifier alsoreceives complementing signals from the track 83, via sets of terminals87. The amplifier 86 operates in a manner similar to amplifier 78,directing each hundreds digit signal to the appropriate one of a set 88of ten hundreds digit output signal lines,

according to the complementing signal received through the terminals 87.

The assembly 61, may alternatively, comprise a contact track such as isillustrated in FIG. 7, repetitively extended to include one thousanddigits. In such a case the choosing logic device 68 is not required,while an amplifier similar to the amplifier 78 is used instead of theamplifier 70. The amplifier receives digit signals from a logic device.such as is illustrated at 102 in FIGURE 8, together with complementingsignals from the logic device 103. These. complementing signals are alsopassed to the assembly 62 as complementing choosing signals.

A coarser digitizer, preferably of the kind described in ouraforementioned co-pending application, may be coupled, through areduction gear train, to the end 64' of the shaft 64, 64. Such adigitizer may derive choosing signals from the complementing track 83,through the terminal set 89.

If desired, a one hundred division digitizer may comprise assemblies 62and 63, for use with amplifiers 78 and 86, assembly 61 and associateddevices 68 and 70 being omitted. Assembly 62 therefore comprises afourth contact track 90, for providing, at terminals 92, a choosingmeans drive similar to that described in our aforementioned co-pendingapplication. A suitable choosing means (not shown) can then supplychoosing signals to terminals 93.

Any of the digitizer outputs may be inhibited, except on interrogation,by means similar to those described in our aforementioned co-pendingapplication. The choosing device may also similarly be adapted to act asa short term memory.

In use, each assembly always provides two output signals to represent adigit (including zero); the absence of either one or both output signalstherefore indicates a fault.

The output of the digitizers so far described is a full decimal output;a binary coded decimal output may be obtained by applying the fulldecimal output to a diode logic matrix, in known manner. It is thuspossible to provide both a full decimal and a binary coded decimaloutput, simultaneously.

It is preferred, in practice, that a digitizer comprise necessaryisolating diodes; which may be connected for positive or negative signaloutputs, as desired. Choosing means, inhibiting gates and otherassociated electronic circuits are preferably provided as separateitems.

What is claimed is:

1. A reflected half-base digitizer comprising first support means; a setof electrical contacts disposed on the first support means to form aplurality of tracks, the contacts of the tracks in combinationcorresponding to a scale of notation whose digits are separated into acorresponding plurality of groups of complementary digits, each trackbeing related to one group of digits, the contacts being electricallyconnected together and distributed over at least two parallel paths,there being disposed on each path contacts separated from one anotheralong the path each contact extending along its path a distanceequivalent to at least the distance corresponding to two adjacent digitsof the scale; second support means; a brush corresponding to eachcontact path and mounted on the second support means, all the brushesbeing in fixed relationship with one another; movement means forimparting relative movement between the first and second support means,whereby each brush is capable of sequentially connecting with anddisconnecting from the contacts of its associated path, both leading andtrailing edges of the contacts having significance in reading; andconnection means for connecting brush choosing means to the digitizerwhereby, when the true reading of the scale is represented by aparticular digit, the output of the digitizer carries signals relatedonly to the groups of digits including the said particular digit.

'2. A reflected half-base digitizer comprising first support means; aset of electrical contacts disposed on the first support means to form asingle track having at least four contact paths one of which is acomplementary contact path, the contacts of the paths in combinationcorresponding to the digits of a scale of notation, the digits beingconsidered in two complementary groups, the contacts being electricallyconnected together, each contact extending along its path a distanceequivalent to at least the distance corresponding to two adjacent digitsof the scale, the contacts of each path which has a plurality ofcontacts being separated from one another along the path; second supportmeans; a brush corresponding to each contact path and mounted on thesecond support means, all the brushes being in fixed relationship withone another; movement means for imparting relative movement between thefirst and second support means, whereby each brush is capable ofsequentially connecting with and disconnecting from each contact of itsassociated path, both leading and trailing edges of the contacts havingsignificance in reading; and connection means connected to the brushesand the sets of contacts for providing output signals from each of thesaid brushes.

3. A digitizer as claimed in claim 2 wherein the base of the scale isten and wherein there are provided at least five contact paths, three ofwhich have contacts each corresponding to at least two adjacent digitsand longitudinally dimensioned and located with an accuracy at least asgreat as the accuracy with which the scale is to be read.

4. A digitizer as claimed in claim 2 wherein the paths are a set ofconcentric closed circles.

5. A digitizer as claimed in claim 2 wherein there are provided aplurality of contact tracks, each track corresponding to a scale, theseveral scales having bases which are sequentially rising powers of thebase of the lowest scale, the corresponding tracks being joined togetherin sequence so that the joined paths form a set of concentric closedcircles; each set of joined corresponding paths being provided with acommon brush.

6. A digitizer for converting an analogue position into numeralscomprising:

first support means,

a plurality of contacts disposed on said first support means to form atleast a single contact track and to form a plurality of parallel contactpaths in each said track so that each said contact track represents .anumerical scale with a division of length associated with each numeralof said scale with each said contact extending along its path for adistance equivalent to at least the distance corresponding to twoadjacent given divisions of length on said scale, a contact track beingassociated with each of the numerals into which said position isconverted,

brush means associated with each said contact path,

means for applying a source of electrical energy to at least some ofsaid brushes to generate electrical information signals,

means for connecting said brushes and contacts to external means forreceiving said information signals and determining said numerals intowhich said position is converted,

second support means for holding each of said brushes in each of saidtracks in fixed relationship to each other, and

means for causing relative movement between said first and secondsupport means to produce said analog position.

7. A digitizer comprising:

a member carrying a contact track having a plurality of contact paths, ascale of notation adjacent the tracks, contacts (as defined herein)corresponding to the digits of the scale distributed over the paths,each contact extending along its path a distance equivalent to at leastthe distance corresponding to two adjacent digits of the scale; and

a plurality of signal brushes (as defined herein) arranged in a first(even or odd) group and a second (odd or even) group, mounted in fixedrelationship with one another and in movable relationship with thepaths, each path having associated therewith a brush capable ofsequentially connecting with and disconnecting from the contacts of thepath, both leading and trailing edges of the contacts havingsignificance in reading;

the contacts and brushes being so relatively disposed that, in use, eachbrush carries one of two signals, according as the brush is or is notconnected to a contact, combined brush signals being logically relatedto the scale reading, as defined by the position of brushes along thetrack cars being provided whereby said first or second group is chosenin accordance with signals derived from an additional contact path onthe member, and the arrangement of the contacts and brushes being suchthat relative movement therebetween along a brush path will producedifferent combinations of brush signals, one for each digit of thescale, by the connections effected between the contacts and the brushes.

8. A digitizer as claimed in claim 7 the said track having two parallelcontact paths, respectively corresponding to two complementary groups ofdigits comprising the scale.

9. A digitizer as claimed in claim 8, wherein the contacts are soarranged that the choosing signals will be inverted at the center of thescale and/ or at the junction of two scales.

10. A digitizer as claimed in claim 7 arranged as a reflected half-basedigitizer comprising a plurality of contact tracks, the tracks incombination corresponding to a scale of notation whose digits areseparated into two complementary groups, each of which is related to acorresponding contact track;

wherein each track comprises at least two parallel paths, there beingdisposed on each path contacts separated from one another along thepath, and each path has movably associated therewith a brush capable ofsequentially connecting with the contacts on the path, eachcomplementary pair of digits, if the base of the scale is even, or eachcomplementary pair of digits and the center digit, if the base is odd,being associated with one brush;

means being provided for connecting brush choosing means to thedigitizer whereby, when the true reading of the scale is represented bya particular digit, the output of the digitizer carries signals relatedonly to the group of digits including said particular digit.

References Cited UNITED STATES PATENTS 2,873,442 2/1959 Ziserman 340-3473,054,996 9/ 1 962 Spaulding et al 340-347 3,056,956 10/1962 Retzinger340-347 3,070,787 12/1962 Waldron et a1. 340-347 3,143,730 8/1964McIntyre 340-347 MAYNARD R. WILBUR, Primary Examiner J. GLASSMAN,Assistant Examiner

